Support structures, such as wooden poles, are common features along municipal landscapes. These structures are primarily used as support structures for power lines and other utility services, such as telephone cables or fiber optics, and equipment, such as transformers and street lights. While some cities have recently begun installing power lines or cables underground, a significant number of wooden poles remain as the primary support structure. Moreover, burying cables underground can be cost prohibitive. Given the large number of such structures in existence, the ability to preserve the wooden poles and characterize the integrity of the structures over time is paramount, as replacing the poles is labor intensive and can involve considerable costs. In addition, since many of the wooden poles are located in highly populated areas, pole replacement can be disruptive, causing road closures or possible disruption of services and/or slow-down of pedestrian traffic near the affected area.
Preservation techniques for preventing wooden materials from deterioration are used as a primary means for extending their useful life. Most preservation techniques fall into two main classes: 1) oil-borne preservatives, such as creosote, pentachlorophenol in petroleum, and copper napthenate; and 2) water-borne preservatives, such as arsenates of copper, including ammoniacal copper zinc arsenate and chromated copper arsenate. These techniques, however, have not been able to provide fail safe preservation means, particularly for utility poles that are routinely exposed to multiple risk factors. Accordingly, a need for continued monitoring of the structural integrity of these structures is needed.
Numerous factors are associated with the deterioration of utility poles. Because the utility poles support vertical, longitudinal, and transverse loads caused by wire tension, weight of coupled objects, and wind, the pole's structural characteristics must be monitored over their lifetime to obtain maximum useful life. In order to successfully monitor the structure over a time period, the ability to determine the overall integrity is paramount. Continuous monitoring provides pole owners the capability of preventing, or at least minimizing, unexpected load failure, thereby reducing the risk of pole collapse, human injury, and property damage. Knowing the pole integrity allows pole owners a reliable mechanism to determine if the structure should be repaired or replaced. Knowing the structural integrity of the poles further allows pole owners the ability to predict replacement times, thereby providing better budgeting analysis and accommodations. Characterizing the structural integrity of each pole further allows the owner the capability to remove excess load which could cause immediate failure or deterioration.
While the type of wooden structures used by municipalities may differ, i.e. western red cedar, Douglas fir, other pines, deterioration is common to all types of wooden structures. Most wooden structures are susceptible to various environmental attacks, such as the gradual deterioration resulting from internal damage caused by insect attack. Termites, ants, and wood borers damage the internal composition of the wood structures which is difficult to accurately and properly access through external visualization techniques. The damage caused by the bio-attack often results in a relatively slow decay process, leaving the pole subject to failure at unpredictable times. Wood destroying fungi are another environmental hazard that results in weakening of the integrity of the wood structures. As mentioned previously, such wood structures can be treated to minimize the damage caused by such organisms. However, the chemical preservation procedures are not fail safe, and a mechanism for monitoring the structure's structural integrity and level of damage, if any, while undergoing treatment is needed. In addition, soil can affect the strength of the pole. For example, if the soil contains acid components, the acid destroys timber fibers and leads to the reduction of pole strength at a faster rate than soils that are less acidic. The presence of big cracks, knots, or moisture can also result in the reduction of pole strength. Even if a pole has no defects, the starting strength may be less than the statistical maxim. The present invention provides a reliable and reproducible system to determine the real, starting strength of the pole. For poles not made of wood fibers, other factors may be important. For concrete poles, the corrosion of reinforcement can result in reduction in pole strength.
Environmental conditions, such as extreme heat, cold, moisture, or lack of rainfall can result in accelerated damage as a result of the environmental conditions, or through increase in organism attack. While certain areas may result in faster decay times, a device and method which can determine structural integrity is needed for any structure that is exposed to the external environment. Finally, wooden structure decay can also result from man-made activities. Typically, chemical preservation treatment includes boring and injection of the chemicals into the structure's internal environment. The boring process, any cuts and/or injection sites can form a focus point for damage and decay.
Various inspection and maintenance programs are performed in order to identify and remove damaged wooden structures. Many programs utilize visual inspection as a primary means for determining the integrity of the wooden structures. Since visual assessment requires individuals to visually inspect each structure, this type of analysis is time consuming and labor intensive as the individual must inspect all parts of the structure's external surface and note any indications of possible damage. Visual inspection offers limited useful information in the assessment analysis and can be problematic because the measurements are subjective, deterioration over a period cannot be properly quantified, nor can the underground or internal aspects of the wooden structure be properly accessed.
Other detection methods are known in the art. For example, use of sound is a common mechanism for determining decay in wood structures. Sound based procedures include the use of an instrument which is placed around the periphery of the structure, at positions ranging from the ground level to the top of structure. The characteristics of the sound generated at each strike are evaluated in order to determine the deterioration. This method however, is subjective and the exact level of deterioration can not be properly assessed. If an area is suspected of possible deterioration, the pole is cored to obtain a sample for further evaluation. However, coring a sample from the wood pole allows oxygen, water, and fungi access to the internal environment. U.S. Pat. No. 4,329,882 describes a kit having tools for obtaining a core sample of an underground portion of a wood structure without the need for removing any ground material. Several other methods and/or devices for determining the pole integrity include U.S. Pat. No. 4,495,518, U.S. Pat. No. 4,702,111, U.S. Pat. No. 5,105,453, U.S. Pat. No. 5,804,728, U.S. Pat. No. 7,743,668, and U.S. Patent Application Publication No. 2003/0131674.
Most of the existing methods range from simple sounding testing using a regular hammer to sophisticated techniques and devices capable of visualizing the inner timber structure. However, these testing methods provide for detecting defects only in a specific cross-section or at accessible areas. Devices using such methods can be considered as flaw detectors and fail to properly and comprehensively estimate the actual strength of a wooden pole entirely. While the most accurate method of bending strength determination is to apply a mechanical load to the pole until the pole reaches its breaking point, such approach is destructive and not applicable for in-service poles.
Therefore, what is needed in the art is an improved method and device which allows inspectors to determine the integrity of the structure, the strength of the structure, and the amount of load that can be applied to the structure in its current state which does not result in failure or further damage.